The Azores High (also known as North Atlantic (Subtropical) High/Anticyclone or for short, NASH, the Bermuda-Azores High, or the Bermuda High/Anticyclone in the United States) is a large subtropical semi-permanent centre of high atmospheric pressure typically found south of the Azores in the Atlantic Ocean, at the Horse latitudes. It forms one pole of the North Atlantic oscillation, the other being the Icelandic Low. The system influences the weather and climatic patterns of vast areas of North Africa and Europe, and to a lesser extent, eastern North America. The aridity of the Sahara Desert and Mediterranean Basin is due to the subsidence of air in the system.
In summer, the central pressure hovers around 1024 mbar (hPa). When it moves north towards the Iberian Peninsula it causes ridging to develop for short periods across northern France, Benelux, Germany and southeastern United Kingdom. This brings hot and dry weather to these areas normally affected by prevailing westerlies. The Azores High (as it is known in Europe) is known more commonly as the Bermuda High in the USA because of the strong westward ridging that develops near Bermuda, usually after the summer solstice. This can contribute to intense heat waves in the eastern United States and, spotty drought. Before the onset of winter, the High moves south of the Azores, allowing low pressure systems to invade the Iberian Peninsula and the Mediterranean.
This high pressure block exhibits anticyclonic nature, circulating the air clockwise. Due to this direction of movement, African eastern waves are impelled along the southern periphery of the Azores High away from coastal West Africa towards the Caribbean and Central America, favoring tropical cyclogenesis, especially during the hurricane season.
An atypical displacement of the Bermuda-Azores High often leads to unusual tracks of tropical cyclones and wintertime extratropical cyclones. The ridge can be temporarily displaced by intense low pressure systems, and in cases when it is displaced to the north, can lead to devastating storm paths such as the one taken by the New England Hurricane of 1938.
Research into global warming suggests that it may be intensifying the Bermuda High in some years, independently of oscillations such as ENSO, leading to more precipitation extremes across the Southeastern United States. Latitudinal displacement of the ridge is also occurring, and computer models depict more westward expansion of the anticyclone in the future. However, during the winter of 2009–2010, the Azores High was smaller, displaced to the northeast and weaker than usual, allowing sea surface temperatures in the Central Atlantic to increase quickly.
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